The present invention relates to a discharge lamp operating apparatus for operating a discharge lamp (in particular, fluorescent lamp). The present invention also relates to a dimmable self-ballasted fluorescent lamp.
Fluorescent lamps are characterized by a higher efficiency and a longer life than those of incandescent lamps, and have been used in a wide range of application such as for household illumination. In particular, self-ballasted fluorescent lamps that hardly have flickers and are capable of starting to operate instantly and in which a high frequency inverter ballast and a fluorescent lamp are formed as one unit can be mounted on a socket for incandescent lamps as they are, so that there is an increasing demand for the self-ballasted fluorescent lamps in view of energy saving and natural resources saving.
FIG. 4 shows an example of the structure of a self-ballasted fluorescent lamp. The self-ballasted fluorescent lamp shown in FIG. 4 includes a fluorescent lamp 101, a lamp base 102 such as E26 type for incandescent lamps, and a circuit substrate 103. In the circuit substrate 103, wiring for a high frequency inverter ballast is formed, and circuit components 106 are provided. The circuit substrate 103 is accommodated in a case 104, and the lamp base 102 is provided in one end of the case 104. A translucent globe 105 is provided below the case 104 so as to enclose the periphery of the fluorescent lamp 101.
The fluorescent lamp 101 has a structure, for example, shown in FIG. 5. FIG. 5A schematically shows the upper surface of the fluorescent lamp 101, and FIG. 5B schematically shows the side face of the fluorescent lamp 101.
The fluorescent lamp 101 shown in FIG. 5 includes a glass bulb 107 whose inner face is coated with a phosphor, and both ends of the glass bulb 107 are sealed with filament electrodes 108 and 109. Electrode lead wires 110 and 111 are electrically connected to the filament electrodes 108 and 109. Four U-shaped glass bulbs 107 are arranged to form a square shape when viewed from the upper face, and connected to adjacent bulbs with a bridge 112. Mercury and rare gas such as argon are enclosed in the glass bulb 107. In addition, amalgam 113 is enclosed to control the vapor pressure of mercury during operation.
The high frequency inverter ballast has a structure, for example, as shown in FIG. 6. The high frequency inverter ballast shown in FIG. 6 includes a line filter 115 connected to an AC power 114, a rectifying circuit 116, a smoothing capacitor 117, a driving circuit 118, and FETs 119 and 120, which are switching elements, a chalk coil 121, and capacitors 122 and 123. Coils 124 are secondary windings of the chalk coil 121.
The line filter 115 prevents high frequency noise from flowing out to the AC power 114, and the rectifying circuit 116 and the smoothing capacitor 117 convert an AC voltage to a DC voltage. The FETs 119 and 120 turn on and off in response to a signal from the driving circuit 118, and thus the DC voltage from the smoothing capacitor 117 is converted to a high frequency AC voltage. The frequency of the high frequency AC voltage depends on the frequency at which the FETs 119 and 120 turn on and off, and generally it is set to about 50 to 80 kHz. The chalk coil 121, the capacitors 122 and 123, and the fluorescent lamp 101 form a load circuit that supplies the high frequency power to the fluorescent 101, and the lamp current that is to flow through the fluorescent lamp 101 is limited by the chalk coil 121, which is a current limiting element. The secondary windings 124 supply a preheating current to the filament electrodes 108 and 109 of the fluorescent lamp 101 by an induced voltage generated by the current flowing through the chalk coil 121.
In the circuit substrate 103 as shown in FIG. 4, multiple circuit components 106 are provided, but in the drawing, only typical components are shown. The fluorescent lamp 101 and the circuit substrate 103 in FIG. 4 are electrically connected to each other through connection pins provided on the circuit substrate 103 by for example, the approach of wrapping with the electrode lead wires 110 and 111 shown in FIG. 5B. The lamp base 102 and the circuit substrate 103 are electrically connected, and power is supplied by threading the lamp base 102 into a socket for incandescent lamps to operate the fluorescent lamp 101.
The self-ballasted fluorescent lamp shown in FIG. 4 can be exchangeable directly with an incandescent lamp, so that the self-ballasted fluorescent lamp has been widely used for the same applications as for incandescent lamps. As it has been used increasingly in a wide range, the needs for dimming in the self-ballasted fluorescent lamp as in the incandescent lamps have emerged. Unlike the incandescent lamps that can be dimmed simply by adjusting the amount of power, it was technically very difficult to dim self-ballasted fluorescent lamps, which are discharge lamps. However, in recent years, a dimmable self-ballasted fluorescent lamp has been developed (e.g., see Japanese Laid-Open Patent Publication No. 11-111486), and the needs as described above have come to be met.
However, for dimmable self-ballasted fluorescent lamps, a member having a dimming function has to be further provided in a compact self-ballasted fluorescent lamp, so that it is more difficult to produce the dimmable self-ballasted fluorescent lamp than a self-ballasted fluorescent lamp without a dimming function. It goes without saying that it is more difficult to produce the self-ballasted fluorescent lamp than an ordinary discharge operating apparatus that can be provided with a discrete ballast.
When the inventors of the present invention investigated self-ballasted fluorescent lamps that were found to be defects during production, it was turned out that the defects were generated by the following defect factor. Referring to FIG. 5, in the process of assembling the fluorescent lamp 101, the lamp base 102, the circuit substrate 103, the case 104, and the globe 105 into one unit, the electrode lead wires 110a and 110b or 111a and 111b may be brought into contact with each other.
Since the electrode lead wire 110 and 111 have to be electrically connected to the connection pins on the circuit substrate 103, these electrode lead wires are generally not subjected to a treatment for insulating coating or the like. Therefore, when these electrode leads wires are brought into contact with each other, the electrode lead wire 110 and 111 are provided with a contact resistance at the contact point. The contact resistance value changes depending on the state in which the electrode lead wire 110 and 111 are brought into contact. When the electrode lead wires 110 and 111 are brought into contact, the current output from the secondary windings 124 depends on the contact resistance value.
When the contact state of the electrode lead wires 110 and 111 is a complete short-circuit, that is, the contact resistance value is substantially 0xcexa9, a large current of several tens A flows from the secondary windings 124, so that the chalk coil 121 and the secondary windings 124 fail substantially instantly and the ballast stops (hereinafter, referred to as xe2x80x9clarge current failure modexe2x80x9d). When the contact resistance value is such that a current of about 3 A flows through the secondary winding 124, the fluorescent lamp 101 is operated while consuming about several W of power at the contact point and the ballast continues to be operated. Meanwhile, the temperature at the contact point reaches several hundred xc2x0 C., and the adjacent circuit substrate 103, the case 104 and the like may be excessively heated (hereinafter, referred to as xe2x80x9csmall current failure modexe2x80x9d).
With respect to these problems, the inventors of the present invention found that if the electrode lead wires 110a, 110b, 111a, and 111b are covered with an insulating tube or the like in the assembly process to prevent the electrode lead wire 110a or 111a from being in contact with the electrode lead wire 110b or 111b, respectively, these problems may be avoided. However, this measure causes new problems such as an increase in the number of production processes and the cost due to the insulating tubes.
On the other hand, if it is attempted to remove defects by inspection without covering them with the insulating tubes, the following problems may be caused. In the case of the large current failure mode, a product is determined as a defect at an inspection before delivery, so that defects are not distributed in the market. However, in the case of the small current failure mode, it is difficult to determine a product as a defect, so that some defects may be distributed in the market. A sufficient measure has been provided in the unlikely event that this were to occur, but naturally it is better to prevent this problem from occurring in any case.
Therefore, with the foregoing in mind, it is a main object of the present invention to provide a dimmable self-ballasted fluorescent lamp and a discharge lamp operating apparatus that can prevent inexpensively the unwanted contact problem that is likely to occur in the assembly process.
A dimmable self-ballasted fluorescent lamp of the present invention is a self-ballasted fluorescent lamp obtained by forming a fluorescent lamp, a ballast that is electrically connected to the fluorescent lamp and a lamp base as one unit. The ballast includes a preheating current supply circuit for supplying a preheating current to the fluorescent lamp; an inverter circuit portion for supplying a high frequency AC power to the fluorescent lamp; and a control circuit portion for controlling a driving frequency of the inverter circuit portion. The ballast is provided with an output current limiting element for limiting an output current from the preheating current supply circuit.
It is preferable that the output current limiting element is constituted with a circuit element that becomes in an open state when an output current flows at a predetermined value or more, and the circuit element is a capacitive element or an inductive element.
The output current limiting element may be constituted with a circuit element that becomes in an open state when an output current flows at a predetermined value or more, and the circuit element may be a chip resistor.
In one embodiment of the present invention, the output current limiting element is constituted with a circuit element that becomes In an open state when an output current from supply means for supplying a preheating current to the fluorescent lamp flows at a predetermined value or more. The preheating current supply circuit includes a closed circuit network for supplying a preheating current to the fluorescent lamp. The circuit element is arranged on the closed circuit network.
In one embodiment of the present invention, the closed circuit network includes a secondary winding of an inductor element that functions as a current limiting element for limiting a lamp current that is to flow through the fluorescent lamp.
According to another aspect of the present invention, a discharge lamp operating apparatus includes a discharge lamp and a ballast for operating the discharge lamp. The ballast includes preheating current supply means for supplying a preheating current to the discharge lamp; and output current limiting means for limiting an output current from the preheating current supply means.
In one embodiment of the present invention, the discharge lamp operating apparatus is a self-ballasted fluorescent lamp obtained by forming a lamp base, the ballast that is electrically connected to the lamp base, and the discharge lamp as one unit. The output current limiting element is constituted with a circuit element that becomes in an open state when an output current flows at a predetermined value or more.
According to the present invention, an output current limiting element for limiting an output current from a preheating current supply circuit is provided in a ballast, so that the problem of unwanted contacts, which are likely to occur in the assembly process, can be prevented at a low cost. Furthermore, a capacitive or inductive element is used as the output current limiting element, so that a power loss of the output current limiting means in the regular state where the electrode lead wires are not in contact can be reduced.